This invention relates generally to the detection of submerged objects and more particularly to the detection of objects beneath the surface of environmental waters by signal energy radiation.
The detection of submerged objects, such as underwater obstructions to marine travel including sunken vessels, debris, large sea life, etc., by echo-ranging techniques involving the radiation of signal energy, is generally well known in the art. Such systems for detecting underwater objects from a moving platform in the form of a marine vessel or an airborne aircraft such as a helicopter, were heretofore of an optical type or an acoustical type. Optical types of systems heretofore involved the exclusive use of electromagnetic radiation for the detection of submerged objects near the surface of environmental waters. In the latter type of remote detection system, the radiation emitted from a laser transmitter, for example, would suffer considerable attenuation during propagation through the water toward the object and more severe attenuation during reflection from the object as an echo to be picked up by the receiver. The severity of such attentuations would depend upon the concentration of particulate matter in the water to thereby limit the detection range through water having any significant optical turbidity.
The signal attenuation problem usually associated with optical systems is less severe in acoustical detection systems operating at frequencies below 100 KH.sub.z for example. Nevertheless, such acoustical detection systems suffer from water volume and water surface reverberation problems. In particular, water surface reverberations compete with the echoes from an object close to the water surface so as severely limit the detection range.
It is therefore an important objective of the present invention to provide a remote object detection system involving the transmission and return of radiated signal energy through the body of water within which the object is located without the optical attenuations associated with electromagnetic radiation systems or the problems involving surface and volume reverberation associated with acoustical detection systems as aforementioned.